diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index de5cd10..a3b791f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,8 +1,5 @@
 name: ci
 
-env:
-  HOMEBREW_NO_INSTALL_CLEANUP: 1
-
 on:
   push:
     paths:
@@ -45,6 +42,8 @@ jobs:
     - name: install prereqs (macOS)
       if : runner.os == 'macOS'
       run: brew install ffmpeg
+      env:
+        HOMEBREW_NO_INSTALL_CLEANUP: 1
 
     - name: Install winget
       if: runner.os == 'Windows'
diff --git a/README.md b/README.md
index 62852b8..9d348d5 100644
--- a/README.md
+++ b/README.md
@@ -205,7 +205,9 @@ JSON:
 * `camera_size`: camera resolution -- find from `v4l2-ctl --list-formats-ext` or camera spec sheet.
 * `camera_fps`: camera fps -- found from command above or camera spec sheet
 
-Stream to multiple sites, in this example Facebook Live and YouTube Live simultaneously:
+Stream to multiple sites. This uses FFmpeg
+[-f tee](https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs#Teepseudo-muxer).
+For example, Facebook Live and YouTube Live simultaneously:
 
 ```sh
 python -m pylivestream.camera youtube facebook ./pylivestream.json
diff --git a/src/pylivestream/base.py b/src/pylivestream/base.py
index f9aa039..ca4834a 100644
--- a/src/pylivestream/base.py
+++ b/src/pylivestream/base.py
@@ -103,7 +103,12 @@ def startlive(self, sinks: list[str] | None = None):
             run(self.cmd)
         elif len(sinks) == 1:
             run(self.cmd)
-        else:  # multi-stream output tee
+        else:
+            """
+            multi-stream output tee
+            https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs#Teepseudo-muxer
+            https://trac.ffmpeg.org/wiki/EncodingForStreamingSites#Outputtingtomultiplestreamingserviceslocalfile
+            """
             cmdstem: list[str] = self.cmd[:-3]
             # +global_header is necessary to tee to multiple services
             cmd: list[str] = cmdstem + ["-flags:v", "+global_header", "-f", "tee"]
@@ -115,7 +120,8 @@ def startlive(self, sinks: list[str] | None = None):
                 if self.vidsource == "file":
                     # picks first video and audio stream, often correct
                     cmd += ["-map", "0:v", "-map", "0:a:0"]
-                else:  # device (Camera)
+                else:
+                    # device (Camera)
                     # connect video device to video stream,
                     # audio device to audio stream
                     cmd += ["-map", "0:v", "-map", "1:a"]
diff --git a/src/pylivestream/ffmpeg.py b/src/pylivestream/ffmpeg.py
index ad2c947..3c85270 100644
--- a/src/pylivestream/ffmpeg.py
+++ b/src/pylivestream/ffmpeg.py
@@ -21,6 +21,7 @@ def __init__(self):
         # default 8, increasing can help avoid warnings
         self.QUEUE = ["-thread_queue_size", "8"]
 
+        # https://trac.ffmpeg.org/wiki/StreamingGuide#The-reflag
         self.THROTTLE = "-re"
 
     def timelimit(self, t: str | int | float | None) -> list[str]:
diff --git a/src/pylivestream/stream.py b/src/pylivestream/stream.py
index e242a7e..2023ab0 100644
--- a/src/pylivestream/stream.py
+++ b/src/pylivestream/stream.py
@@ -212,17 +212,16 @@ def audioOut(self) -> list[str]:
         https://www.facebook.com/facebookmedia/get-started/live
         """
 
-        if not (self.audio_bps and self.acap and self.audio_chan and self.audio_rate):
-            return []
+        o = []
+
+        if self.audio_codec:
+            o += ["-codec:a", self.audio_codec]
+        if self.audio_bps:
+            o += ["-b:a", str(self.audio_bps)]
+        if self.audio_rate:
+            o += ["-ar", str(self.audio_rate)]
 
-        return [
-            "-codec:a",
-            self.audio_codec,
-            "-b:a",
-            str(self.audio_bps),
-            "-ar",
-            str(self.audio_rate),
-        ]
+        return o
 
     def video_bitrate(self) -> None:
         """